Real image displays can be separated into three categories: cathode ray tubes (CRT), flat panel displays, and projection displays. Currently, CRT displays range from 1-40 inches along the image diagonal. These displays have good image quality and can be manufactured economically. The shape of the display requires a depth that can exceed the length of the image diagonal for high resolution graphic displays. The displays are bulky, especially for sizes above 20 inches because the wall thickness of the glass must be increased to withstand the atmospheric pressure. CRTs are popular in the desktop monitor market where the common length of the image diagonal is 14-17 inches.
Flat panel displays are used in many portable applications. They are thin and light in weight but have an image quality that is inferior to the CRT. At this time, the majority of displays are used in applications requiring 2-12 inches along the image diagonal. Flat panel displays are more costly to manufacture than the CRTs.
As a result, display applications that require an image size above 40 inches are dominated by projection displays: either front or rear. Both technologies can create an image by one of two methods: using three small high brightness monochromic CRTs for red, green, and blue (RGB) or creating a color image via a spatial light modulator. These projection systems have low image brightness and are costly to manufacture.
It is not economical to reduce the conventional rear projection display to 17-20 inches along the image diagonal. The cost of the light valve is dominated by the drive circuitry. To illustrate, the drive circuitry of an XGA display (768.times.1024.times.3) is approximately $120 regardless of the screen size. A 70W metal halide arc lamp capable or producing 5000 lumens with its corresponding power supply, ballast, and hot reignition capability are required. The total cost is prohibitive and unattractive compared to the OEM cost of a 17 inch CRT.